1. Field of the Invention
This invention relates to polymeric compositions useful for sizing or protecting siliceous materials, such as glass fibers used to reinforce organic resins and for promoting adhesion between the glass fiber reinforcement and organic resins, and particularly relates to compositions containing polyester aminoorganosilanes and/or their acid salts wherein the silane-modified polyesters include an effective level of polyalkylene glycol monomer units.
2. Description of Related Art
Glass strands, mats and roving are used widely to reinforce resinous molding compositions. Probably the biggest application concerns the reinforcement of thickened, polymerizable polyester resins.
Glass fiber strands are formed from numerous individual fine glass fibers generally produced by drawing molten glass through small orifices. As the fibers are being drawn, they typically are coated with a sizing composition to protect individual fibers from abrasion (lubrication) or other factors causing surface defects (corrosion), to facilitate the binding of multiple fibers into strands (binder) and to enhance the adhesion between the glass fiber reinforcement and the organic resin (compatibilization/coupling).
As the sized fibers are drawn and collected to form strands, the strands generally are wound onto a forming tube. Once the wound sized glass fiber strands have built up to the desired extent on the forming tube, the assembly or forming package is heated in an oven, sometimes under a reduced pressure, to dry and cure the sizing.
U.S. Pat. No. 3,936,285 discloses a composition suitable for sizing glass fibers containing a more or less equal blend of two polyester resins, one a water-soluble, unsaturated polyester resin salt, which when crosslinked is insoluble in aromatic solvents, and the other one a water-dispersible, unsaturated polyester resin which is insoluble in the first resin. The composition also includes a plasticizer, a combination of silane coupling agents and a low molecular weight thermoplastic polymer.
U.S. Pat. No. 4,122,074 describes certain polyester aminoalkylalkoxysilane polymers and their organic acid salts. The silane-modified polyesters are formed by reacting an unsaturated polyester with an aminoalkylalkoxysilane. These polymers are used as a sizing composition to compatibilize and render adherent inorganic siliceous materials, such as glass strands, used to reinforce polyester molding resin. In U.S. Pat. No. 4,273,694 the stability of such polyester aminoalkylalkoxysilane polymers used for forming aqueous dispersions is improved by amine neutralization with strong acids. While these materials satisfy many of the requirements of a good glass size, they tend to impart insufficient stiffness to the sized fibers and exhibit too high a solubility in organic solvents making them less suitable for use as a size for glass fiber reinforcement of thickened, polymerizable polyester resins, particularly for sheet molding compound (SMC), and bulk molding compound (BMC).
To improve the stiffness of the sized glass strands and reduce the degree of extractability of the size, U.S. Pat. No. 4,340,520 describes blending certain polyalkylene glycol polymers with the prior art polyester aminoalkylalkoxysilane polymers and their acid salts. Though leading to improvements in these properties of the sized glass strands, the polyalkylene glycol in such polymer blends, exhibits a tendency to migrate when the coated strands are dried and cured. When migration of polyalkylene glycol occurs it creates a nonuniformity in the degree of cure of the size in the forming package (as measured by its solubility in organic solvents). For example, sized fiber strands proximate the exterior of the package are more cured and stiffer than sized fiber strands in the interior of the package. A different kind of a migration problem also confronts other commercial sizing compositions such as those described in U.S. Pat. No. 3,936,285, where there is a noticeable difference in the level of coating (as measured by loss on ignition) across the forming package. Nonuniformities caused by migration in the size coating and cure cause nonuniform properties of the reinforced polyester article.
It now has been discovered that the migration problem encountered when employing the two component size of U.S. Pat. No. 4,340,520 can be solved by replacing its two component polymeric mixture with a single polymer component size essentially containing a polyester aminoorganosilane and/or its acid salt wherein the polyester portion of the polymer contains a polyalkylene glycol chain segment.